Theory of dispersion of an ultrafast electron wavepacket generated by a femtosecond laser pulse in a nanostructure

Abstract

The temporal dispersion of ultrafast electron wavepacket generated by using femtosecond laser irradiation at sharply-etched metal nanoprobe approached to a dielectric substrate is theoretically studied. A clear broadening and splitting of the wavepacket in the time domain is observed when it arrives at the substrate under low peak electric field, short wavelength conditions, which is owing to the broad kinetic-energy distribution of electrons generated in different emission phases and to the different dynamics of sub-cycle electrons and quiver electrons. Such broadening is proven to be reduced down to 1 fs when either the peak electric field of the incident laser pulse becomes higher, or wavelength becomes longer. Simultaneously, the number of peak of the electron wavepacket in time domain is reduced due to the reduced generation yield of quiver electrons.